1. Filed of the Invention
The present invention relates to a noise reduction device and a noise reduction method, which reduces noise of a video signal by correcting signal values of pixels based on a relation between a target pixel and each of a plurality of peripheral pixels which are located around the target pixel. The present invention also relates to an image pickup apparatus having the noise reduction device. Particularly, the present invention relates to a noise reduction device and a noise reduction method which reduces noise of a video signal containing a color signal, and to an image pickup apparatus having the noise reduction device.
2. Description of the Related Art
A video signal obtained by image pick-up by use of a solid-state image pickup device such as a CCD (Charge Coupled Device) and a C-MOS sensor is a signal in which noise is superimposed on pixels, due to variations in characteristics among the pixels, influence of wiring resistances and the like. Therefore, a noise reduction circuit to reduce the noise superimposed in the video signal output from the solid-state image pickup device has heretofore been provided in a circuit at a rear stage behind the solid-state image pickup device.
In most of such noise reduction devices, by use of each of the signal values of a plurality of peripheral pixels existing within a predetermined range, a center of which is a target pixel to be subjected to a noise reduction processing, and by use of a correlation between the target pixel and each of the peripheral pixels, a signal value in which noises are averaged is obtained. This signal value is used as a signal value of the target pixel. At this time, presence of the correlation between the target pixel and each of the peripheral pixels is judged by comparing the difference of the signal value between the target pixel and each of the peripheral pixels with a threshold value. Subsequently, the number of peripheral pixels correlated with the target pixel is counted, and a sum of the signal values of peripheral pixels correlated with the target pixel and the signal value of the target pixel is obtained. An average value obtained by use of the number of peripheral pixels and the sum of the signal values of the pixels is used as the signal value of the target pixel, whereby noises are removed.
In addition, as a technology using the signal values of the peripheral pixels correlated with the target pixel as described above, a noise reduction device has been proposed, in which a threshold value to judge the presence of the correlation and an area where the peripheral pixels used are included are switched based on the signal value of the target pixel, any one of an average value and a variance for one frame, and an average value of high frequency components (see Japanese Patent Laid-Open No. 2003-179779).